Electro-thermal regulating device



y '3958 A. NEGROMANTI 2,841,681

ELECTRO-THERMAL REGULAIING DEVICE Filed May 31, 1955 United. ratesPatent ELEQ'lilliiQ-THERMAL G DEV Antonie Negromanii, Milan, rtaiyApplication May 31, 1955, Serial No. 519;,h94

priority, application Great Britain June 3, 195

d (Ilaims. {CL fewit This invention relates to an electro-thermal devicefor regulating at will, and from a distance, the temperature of anelectrically heated body, without having recourse to the usualthermostatic valves or like voluminous devices placed in close contactwith the heated body.

A preferred form of construction of the invention is diagrammaticallyillustrated merely by way of example by the accompanying drawings,wherein by way of example the body of which the temperature is to beregulated and controlled is the worloplate of an ordinary smoothing orpressing iron.

In these drawings, Figure l is a circuit diagram of the device; and

Figure 2 is a plan view of the worloplate of a smooth ing iron thermallyregulated according to the present invention.

it will be assumed that the heating circuit 1 has a temperaturecoetiicient of zero and a resistance of 100 ohms; 2 denotes a circuithaving a variable temperature cociiicient, preferably positive, and aresistance of ohms; .3 denotes a circuit the resistance of which can bevaried by means of a sliding contact, which will be assumed to be placedin such a position that the circuit has a resistance of 150 ohms; and tis a circuit having a resistance of 3000 ohms and a Zero temperaturecoefiicient. The circuit 5 is by way of example represented as anincandescent lamp.

These circuits, connected as indicated in Figure l, constitute the fourarms of a Wheatstone bridge which is perfectly balanced when the heatingcircuit is cold. It will be obvious that the ohmic values assigned tothe four circuits may diflfer from those enumerated, provided theysatisfy the above condition. Now let it be assumed that the oppositeangles 6 and 7 of the bridge are supplied with current from a source 5,through an electro-thcrmal or electro-magnetic relay 8, the excitationcircuit 9 of which is inserted between the other two opposite angles 10and 11 of the bridge.

The body of which it is desired to control and regulate the temperatureat will is assumed to be, for instance the worlc-plate 12 of a 400-wattsmoothing iron supplied at a voltage of 200, and the circuits 1 and 2will be arranged on this plate, preferably in the manner indicated inFigure 2.

In a separate casing 13 are arranged the circuits 3 and 4 and the relay8, and by means of conductors 14, 15 and 16 these are connected with thecircuits 1 and 2 in the manner indicated in Figure 1. By 17 is denoted acurrent-supply cable leading to a current plug 218.

The method of operation of the device will now be readily understood.The circuit 2, which may be described as the control circuit, will notbecome heated by Joule effect, in view of the smallness of its ohmicresistance, but it will be heated by the plate 12, with which it is inclose contact, and will assume the temperature of the plate. To anyincrease in this temperature there Patented July 1, 1958 En. willcorrespond an increase in the ohmic resistance of the circuit 2, untilit reaches a value for which there will be a sufficient voltagedifference between the angles it) and 11 to give rise to a currentstrong enough to energise the relay 3, with consequent interruption ofthe current.

The possibility is provided of varying the period of interruption of therelay 8, so as to have practically constant temperatures on the plate12. By varying the sensitiveness of the relay 8, for instance byinserting in its excitation circuit 9 a variable auxiliary resistance,the value or" the energisation current will also be varied, andtherefore also the temperature that will be maintained on the plate.This temperature can be read off on an appropriate dial.

A similar result may be obtained by k eping the sensitiveness of therelay 8 constant and varying the ratio between the arms of the bridge bymeans of the abovementioned slidable contact on the resistance arm 3.

I claim:

1. An electro-thermal device for regulating the temperature of anelectrically heated body, comprising four circuits forming together thefour arms of a Wheatstone bridge, one arm of the bridge aloneconstituting the heating circuit that beats the said body, and having aZero temperature coeiiicient, and one arm adjacent thereto constitutingalone a control circuit, this arm having a variable temperatureCO6ffilI1i and a negligible ohmic resistance, and this control circuitas well as the heating circuit being in close contact with the body thetemperature of which is to be controlled, an electrical relay, and meansfor supplying electric current through the said electrical relay to twoopposite angles of the Wheatstone bridge, said two arms being connectedin series across the means for supplying electric current, the other tWoarms of the bridge being connected in ries across said means, remotefrom and out of heat exchange relation with said body, the excitationcircuit of the said relay being inserted directly between the remainingtwo opposite angles of the Wheatstone bridge, and being adapted to openthe heating circuit upon a predetermined temperature of the body that isbeing heated being exceeded.

2. An electro-thermal regulating device as claimed in claim 1, furthercomprising a sliding contact for varying the resistance of that arm ofthe Wheatstone bridge which is opposite to the heating resistance.

3. An electro-thermal regulating device as claimed in claim 1, the armof the Wheatstone bridge opposite to the control circuit having a zerothermal coetiicient and an ohmic resistance which is substantiallygreater than that of any other arm of the bridge.

4. An electro-thermal regulating device as claimed in claim 1, saidother two arms of the Wheatstone bridge being arranged in a separatecasing.

References Cited in the file of this patent UNITED STATES PATENTS1,276,589 Steinmetz Aug. 20, 1918 1,994,076 Kuhle et a1 Mar. 12, 19352,093,745 Westell Sept. 21, 1937 2,163,297 Waage June 20, 1939 2,278,633Bagnall Apr. 7, 1942 2,510,039 Rudahl May 30, 1950 2,673,917 WoodlingMar. 30, 1954 2,732,477 Runaldue et a1. Jan. 24, 1956 FOREIGN PATENTS144,669 Great Britain Sept. 9, 1921 338,880 Great Britain Nov. 18, 1930

